1. Field of the Invention
The invention relates to an electrochemical analysis system for the analytical determination of a constituent of a sample, in particular for the analysis of body fluids such as blood or urine. The system consists of disposable analysis elements, which are thrown away after use, and an evaluation unit.
2. Description of the Related Art
Analysis by means of disposable analysis elements has acquired great importance above all in the medical field. Compared with the analytical methods using liquid reagents which were exclusively the norm previously, it is distinguished above all by ease of handling. Analyses are thus able to be carried out with great accuracy by relatively untrained laboratory staff, or even by the patient himself. The evaluation units are comparatively inexpensive, and it is therefore possible to carry out the analysis "close to the patient" in the doctor's surgery or at the hospital station.
The analysis elements contain reagents which on contact with the sample lead to a physically detectable change characteristic of the analysis. In the case of the analysis elements most commonly used in practice the reaction of the reagents with the sample leads to a colour change, which is analysed visually or by reflection photometry.
In addition, there have already existed for a long time developments aimed at applying electrochemical analysis methods, in particular analysis by means of enzyme electrodes, to systems with disposable analysis elements. Such analysis elements have on an isolating carrier in a sample application zone at least one sensor with a working electrode and a reference electrode. The electrodes are connected via connecting leads to connecting contacts, which are located in a connection zone of the analysis element. There may be measured from the connecting contacts the variation in an electrical property of the analysis element, said variation being characteristic of the analysis.
An example of such an analysis element is described in U.S. Pat. No. 4,225,410. It has a large number of different sensors on a single isolating carrier, in order to enable several different analyses to be conducted simultaneously on a sample (for example a drop of blood).
Use is made in this connection of various measuring principles known from the field of electrochemical analysis. In particular a distinction is drawn between potentiometric and amperometric sensors. In the case of potentiometric sensors a voltage is obtained by electrochemical means, which may be measured with high resistance at the connecting contacts. In the case of amperometric sensors, for which the present invention is particularly advantageous, a current flowing at a defined voltage forms the electrical property measurable at the connecting contacts.
The evaluation units of such systems have an analysis element connection plug for the electrical connection to the connecting contacts of the analysis elements and a measuring and evaluation circuit. The measuring and evaluation circuit serves to measure the signal to be measured and to convert the measured value into an analytical value. Various methods are known for the conversion, a microprocessor usually being used. The results are usually represented on a display located on the evaluation unit. They may also be passed to a separate central processing unit and be displayed and/or recorded there.